docs: def wait_for_unit(service_name, timeout=480):
      """Wait `timeout` seconds for a given service name to come up."""
      wait_for_machine(num_machines=1)
      start_time = time.time()
      while True:
          state = unit_info(service_name, 'agent-state')
          if 'error' in state or state == 'started':
              break
          if time.time() - start_time >= timeout:
              raise RuntimeError('timeout waiting for service to start')
          time.sleep(SLEEP_AMOUNT)
      if state != 'started':
          raise RuntimeError('unit did not start, agent-state: ' + state)